1. Field of the Invention
The present invention relates to a surface-emitting semiconductor device used as a light source in optical transmission and optical information processing and more particularly, to a surface-emitting semiconductor device in which the polarization direction of a light-output emitted is confined to one direction.
2. Description of the Related Art
Recently, research has progressed on semiconductor lasers used as a light source in the optical transmission and optical information processing fields. Among the semiconductor lasers, a surface-emitting semiconductor laser features as follows;
(1) Monolithic formation of the cavity is possible, PA1 (2) Test of the lasers can be made in a semiconductor wafer unit before separation into chips, PA1 (3) Dynamic single wavelength operation is expected, PA1 (4) A large radiation area and a narrow circular optical beam are possible, PA1 (5) A densely packed two-dimensional laser array can be provided, and PA1 (6) Three-dimensional laser array device can be integrated by layered structures.
Iga and other researchers played a leading role in the research of the surface-emitting semiconductor laser, which are summarized including its historical aspect in the report by Iga and et al in "Journal of Quantum Electronics" Vol 24, P. 1845, September 1988.
Such surface-light-emitting optoelectronic functional devices that make the best use of advantages of the surface-light-emitting semiconductor devices as shown above are expected to make the two-dimensional parallel optical information process possible for large-capacity information processes. A vertical-to-surface transmission electrophotonic device with a vertical-cavity, which is one type of the surface-light-emitting optoelectronic functional device, is disclosed in detail in the report by Numai in "Applied Physics Letters", Vol. 58, P. 1250, March 1991.
The conventional surface-emitting semiconductor devices described above, however, give rise to the following problems as:
First, since the optical waveguide is not provided along the travelling direction of light, the polarization direction of an output laser beam is determined depending on a difference in loss or gain in the cavity due to a slight asymmetry of the device structure. As a result, uniformity of the polarization direction of the device cannot be made.
Furthermore, when the surface-emitting semiconductor device is optically coupled with any other optical circuit element, it is required to confined the polarization direction of the laser beam emitted to a specific direction in order to improve the coupling efficiency.
In order to solve the above-mentioned problem about the coupling efficiency, an example of a surface-emitting semiconductor laser is disclosed in the Japanese Non-Examined Patent Publication No. 1-265584, in which a dielectric optical waveguide with a rectangular cross-section perpendicular to its light emitting direction is provided in cladding layers. Due to the rectangular cross-section of the waveguide the polarization direction is confined to a specific direction, however, this semiconductor laser cannot provide a satisfactory polarization characteristic and therefore, a satisfactorily high optical coupling efficiency cannot be obtained.